1. Field of the Invention
The invention relates to a sliding support structure for a shaft member and, more particularly, to a sliding support structure for a shaft member, which is used for an internal combustion engine, or the like, and which supports a fluctuating load exerted between a sliding surface of the shaft member and a sliding surface of a support member.
2. Description of the Related Art
In general, in a sliding support structure for a shaft member, lubricating oil is supplied to between sliding surfaces of the relatively rotatable shaft member and support member to form a lubricating oil film. Then, a load is supported by an oil film pressure generated in the lubricating oil film to thereby reduce friction loss, prevent wear and seizure of the shaft member and support member and provide noise suppression effect owing to the cushioning function. It is known that these advantageous effects are remarkable as the thickness of the lubricating oil film between the sliding surfaces increases or as the amount of lubricating oil increases.
In order to increase the amount of lubricating oil between such sliding surfaces, there is proposed a technique for forming a large number of narrow grooves or linear marks on an inner peripheral surface of a bearing in a circumferential direction in parallel with one another. For example, Japanese Patent Application Publication No. 2006-329252 (JP-A-2006-329252) describes a rotational sliding structure between a shaft and a bearing in order to reduce energy loss due to shearing resistance of lubricating oil held between the shaft and the bearing. In the rotational sliding structure, circumferential grooves are formed on a rotational sliding surface of at least one of the shaft and the bearing, and an oil repellent film is formed on an inner surface of each groove.
In addition, Japanese Patent Application Publication No. 2007-211956 (JP-A-2007-211956) describes a bearing structure that sufficiently generates a bearing support pressure in a lubricating oil film. In the bearing structure, in a fluid machine, such as a vertical mixed flow pump, the sliding surface of a lower side bearing member and the sliding surface of an upper side bearing member are opposite via a fluid lubricating layer, at least one of the sliding surfaces has an oil-repellent first area that causes a slip flow and a lipophilic second area that causes a slip flow of 0 or smaller than that of the first area, and then the first area and the second area are alternately arranged in a sliding direction or the first area is scattered in the second area.
Note that Japanese Patent Application Publication No. 2007-192330 (JP-A-2007-192330) and Japanese Patent Application Publication No. 2008-223942 (JP-A-2008-223942) describe not a slide bearing but a rolling bearing. In the rolling bearing, grooves are formed on a rolling surface of at least one of raceway surfaces of inner and outer rings of the rolling bearing and rolling surfaces of rolling elements and then an oil repellent film is formed on the grooves.
Incidentally, in a sliding support structure used, for example, in an internal combustion engine for an automobile, the magnitudes and directions of loads exerted respectively on a shaft member and a support member fluctuate during one rotation of the shaft member or support member or during one operation cycle. Unless a predetermined oil film pressure is generated in a gap formed in correspondence with a direction in which the maximum fluctuating load of the fluctuating loads is exerted (hereinafter, this is termed load concentrating direction, and the sliding surfaces of the shaft member and support member, corresponding to the load concentrating direction, are termed load concentrating portions), so-called oil film shortage, or the like, occurs at that portions, resulting in a shift from fluid lubrication into mixed lubrication or boundary lubrication in which the shaft member partially directly contacts the support member. This may cause an increase in friction loss between the shaft member and the support member and, by extension, lead to wear, heating, seizure, or the like. Thus, usually, measures are taken in order to avoid such a situation. For example, a sufficient amount of lubricating oil is supplied, or the diameter of the shaft member and the diameter of the support member are increased or the width of the support member is increased so that the contact pressure between the shaft member and the support member decreases.
However, such measures lead to an increase in size and cost of the sliding support structure, so it is desirable that a sliding support structure generates a sufficient oil film pressure by the sliding support structure itself to thereby make it possible to reduce friction loss.
Note that the rotational sliding structure between the shaft and the bearing, described in JP-A-2006-329252, is a technique for reducing energy loss owing to shearing resistance of lubricating oil held between the shaft and the bearing, and JP-A-2006-329252 does not describe a case where the load concentrating portions are present. In addition, the bearing structure described in JP-A-2007-211956 is of a thrust bearing type in which a load is uniformly exerted on the sliding surfaces of the upper side bearing member and lower side bearing member from an upper side to a lower side, and JP-A-2007-211956 does not describe the type of bearing for a rotary shaft of which the sliding surface has a portion on which a load concentrates.